Signal processing arrangement for a transmitter

ABSTRACT

A signal processing arrangement for a transmitter includes an in-phase modulator configured to receive an in-phase signal (I) and configured to modulate the in-phase signal (I); a quadrature modulator configured to receive a quadrature signal (Q) and configured to modulate the quadrature signal (Q); an in-phase demodulator configured to demodulate the modulated in-phase signal (I) and to output a demodulated in-phase signal (I); a quadrature demodulator configured to demodulate the modulated quadrature signal (Q) and to output a demodulated quadrature signal (Q); an in-phase harmonic filter configured to perform a filtering on harmonics in the demodulated in-phase signal (I) and to output an in-phase digital signal (I); and a quadrature harmonic filter configured to perform a filtering on harmonics in the demodulated quadrature signal (Q) and to output a quadrature digital signal (Q).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No.PCT/CN2017/073503, filed on Feb. 14, 2017, which claims priority toEuropean Patent Application No. EP16157408.2, filed on Feb. 25, 2016,both of which are hereby incorporated by reference in their entireties.

FIELD OF THE INVENTION

The present disclosure relates to a signal processing arrangement for atransmitter. More specifically the present disclosure relates to asignal processing arrangement configured to perform a filtering onmodulation harmonics in a digital RF transmitter.

BACKGROUND

In a traditional analog radio frequency (RF) transmitter, configured toreceive a digital signal, the digital signal is converted into an analogsignal in a digital-to-analog converter (DAC) before any other signalprocessing. The analog signal is then filtered, up-converted andamplified in a linear power amplifier. In the linear power amplifier,the small analog/RF linear signal from the digital-to-analog converterDAC is power enlarged to reach a required output power level. Theamplified signal is then filtered to remove the bandwidth expansioncaused by non-linearity in the power amplification. Finally, theamplified analog/RF signal is output to an antenna. In such atraditional analog/RF transmitter the digital contents of the signal nolonger exist after the conversion in the DAC.

In recent years, digital transmitters (DTX) and digital power amplifiers(DPA) have undergone an extensive development with support fromComplementary Metal Oxide Semiconductor (CMOS) technology. Due to CMOSprocess scaling, digital components can nowadays switch at a highfrequency which even surpasses radio frequencies while still keeping theoperating power low.

This trend provides the motivation to realize a DTX/DPA in a puredigital style. In a DTX/DPA architecture according to conventionaltechnology the demand of using digital signal processing as much aspossible removes the use of a DAC. The DAC is replaced by a digitalup-sampling module to align the data flow bit rate with a digitalcarrier signal (DF_(1o)) later in the DTX/DPA. For the same reason theanalog channel bandwidth filter, is also removed. To compensate for thedigitized signal quantization noise problem, a noise shapingalgorithm/module is mostly used to enhance the signal-to-noiseperformance and during this stage, different DPA modulation algorithmsand different types of DPAs emerged. For example, some may use ADCsampling algorithm and others may use sigma-delta modulation (SDM)algorithm or pulse width modulation (PWM) algorithm, so these algorithmscategorize the DTX/DPA into RF-DAC/RF-SDM/RF-PWM type DTX/DPA.

A DTX/DPA is a kind of transmitter architecture which implement, mostlydigital switching blocks/modules for signal processing/modulation andswitching PA as output stage to amplify output RF power. A DTX/DPA isdifferent from traditional analog/RF transmitter because the internalsignal flow is mostly on/off switching digital characteristics insteadof continuous analog/RF signal.

After the noise shaping processing, the digital signal with multiplelevel representation needs to be further processed and mapped into afully switching on/off (‘0’s or ‘1’s) signal, here the digitaldemodulation module will be used. In this stage, the digital signal willfinally be synchronized into bit rates for the digital carrier signaland is turned into a fully ones/zeros bit sequence. The demodulationmethod can match the previous modulation algorithm but it is alsopossible to use a combination of modulation techniques. As an example,SDM modulation may use ADC or PWM style demodulation methods.

With digitized high speed baseband data according to conventionaltechnology, digital up-conversion and mixing may also be realized indigital style. For example, when ‘1010 . . . 10’ represents 0 degreephase carrier signal, its complementary signal ‘0101 . . . 01’represents 180 degree negative phase signal. And with more bitscombination, I channel and Q channel carrier frequency signal can berepresented in digital bits. This greatly facilitates the RE digitalup-conversion process as a simple ‘AND’ logic operation is sufficient.Since the digital RF I/Q carrier signal has a fixed pattern for everybaseband modulation cycle, a batch process can help to reduce theprocessing clock frequency and parallel data bits are generated duringthis process.

In DTX/DPA architectures, according to conventional technology, adigital signal may be modulated into an in-phase signal and a quadraturesignal. According to conventional technology SDM is used for noiseshaping processing and PWM translation is used as digital demodulationfor the in-phase signal and the quadrature signal, respectively.Connected to the digital demodulation modules are repeaters configuredto data rate match the signal from PWM to the RF carrier signal.Connected to the repeaters is an interleaver module which realizesdigital up-conversion and mixing. The mixed digital signal is then fedto a power amplifier (PA). The PA is connected to a load which isconfigured to radiate RF signal into the surrounding air. A problem withthe DTX/DPA architectures according to conventional technology is thatthe power/hardware cost for the SDM module is high if the SDM module isto operate at a high processing speed. If the SDM operates at a lowprocessing speed the out-of-band noise becomes high. A low processingspeed for the SDM will cause lower noise suppression performance and dueto the operation of the repeater the SDM modulation noise will fold backand increase the in-band noise level. Thus, the SDM actually does notcontribute to the suppression of harmonics.

Another drawback with SDM is that the modulation harmonics are too highand that they are not possible to be attenuated to requested level evenwith an external filter. In some application scenarios, not only in-bandnoise level but also out-of-band noise level should be as low aspossible. Thus, these high modulation harmonics, which are located atmodulation frequency spaced locations, create problems in the describedarrangements according to conventional technology.

Modulation harmonics are quite common for DTX/DPAs which use a differentmodulation processing frequency different from the carrier frequency.Thus, once the modulation frequency is too small, modulation harmonicswill be quite close to the band-of-interest and then the system bandpassfilter will be quite hard to attenuate.

SUMMARY

An objective of the present disclosure is to provide a signal processingarrangement for a transmitter, wherein the signal processing arrangementat least reduces the modulation harmonics problems.

A further objective of the present disclosure is to provide a signalprocessing arrangement for a transmitter, wherein the signal processingarrangement filters out modulation harmonics more efficiently thansignal processing arrangements according to conventional technology.

The above objectives are fulfilled by the subject matter of theindependent claims. Further advantageous implementation forms of thepresent disclosure can be found in the dependent claims.

In the following, an IQ data signal is to be understood as a data signalcomprising an in-phase data signal or an I data signal and a quadraturedata signal or a Q data signal.

According to a first aspect of the present disclosure, a signalprocessing arrangement for a transmitter is provided. The signalprocessing arrangement comprises an in-phase modulator configured toreceive an in-phase signal (I) and configured to modulate the in-phasesignal (I), and a quadrature modulator configured to receive aquadrature signal (Q) and configured to modulate the quadrature signal(Q). The signal processing arrangement further comprises an in-phasedemodulator configured to demodulate the modulated in-phase signal andto output a demodulated in-phase signal, and a quadrature demodulatorconfigured to demodulate the modulated quadrature signal and to output ademodulated quadrature signal. The signal processing arrangement alsocomprises an in-phase harmonic filter configured to perform a filteringon harmonics in the demodulated in-phase signal and to output anin-phase digital signal, and a quadrature harmonic filter configured toperform a filtering on harmonics in the demodulated quadrature signaland to output a quadrature digital signal.

With a signal processing arrangement according to the disclosure theproblem with modulation harmonics will be reduced as the filtration ismore efficient with the configuration according to the disclosure.

In a first possible implementation form of a signal processingarrangement according to the first aspect, the in-phase modulator andthe quadrature modulator are configured to perform pulse code modulationor pulse width modulation. The use of pulse code modulation or pulsewidth modulation is called flat noise modulation.

The use of pulse code modulation or pulse width modulation in thein-phase modulator and the quadrature modulator simplifies the circuitdesign and increases the possible processing speed in comparison withmodulators configured to perform sigma-delta modulation.

Furthermore, the use of pulse code modulation or pulse width modulationin the in-phase modulator and the quadrature modulator improves thenoise shaping performance in comparison with modulators configured toperform sigma-delta modulation.

This is especially true in the case of a second possible implementationform of a signal processing arrangement according to the first aspect orthe first implementation form of the first aspect, wherein the in-phasemodulator comprises cascaded in-phase modulator blocks, and thequadrature modulator comprises cascaded quadrature modulator blocks;wherein each one of the in-phase modulator blocks is configured toprovide a resulting modulated in-phase signal to the in-phasedemodulator, and each one of the quadrature modulator blocks isconfigured to provide a resulting modulated quadrature signal to thequadrature demodulator. The reason for this improvement is that eventhough the sigma-delta modulation can achieve better noise suppressionat a first stage of cascaded in-phase modulator blocks and quadraturemodulator blocks, the inter-stage gain ratio, i.e., the gain ratiobetween blocks, is smaller compared with pulse code modulation or pulsewidth modulation due to larger high frequency noise level. With two orthree stages of cascaded/cascoded architecture the performance of pulsecode modulation and pulse width modulation catches up so that pulsewidth modulation and pulse code modulation provides a better noisesuppression. Also the attenuation of the modulation harmonics is highwith the cascaded modulator blocks according to this aspect.

As for the cascaded modulator blocks, it means the modulation is notfinished in one stage. Since pulse width modulation and pulse codemodulation basically are quantization algorithms, the remains front afirst stage modulator will be treated as un-used noise. In a cascadedpulse width algorithm or pulse code algorithm, after the first stagemodulation, the remaining quantization value will be enlarged by anoptimized ratio and being processed by a modulation algorithm again. Theoutput of this second-stage modulation can be added back to thefirst-stage processed results by multiplying a weight and thus increasethe effective resolution of the total output value. The second stageoutput residue signal may be further processed by the same process asthe second stage did.

In a third possible implementation form of a signal processingarrangement according to the second possible implementation form thein-phase demodulator comprises in-phase demodulator blocks, wherein eachin-phase demodulator block is connected to a corresponding in-phasemodulator block, and the quadrature demodulator comprises quadraturedemodulator blocks, wherein each quadrature demodulator blocks isconnected to a corresponding quadrature modulator block. Theconfiguration of the in-phase demodulator in in-phase demodulator blocksand the quadrature demodulator blocks in quadrature demodulator blocksprovides for a relatively uncomplicated signal processing arrangement.

In a fourth possible implementation form of a signal processingarrangement according to the second or third possible implementationforms, at least one of the in-phase modulator blocks is configured as apulse code modulator or a pulse width modulator, and/or at least one ofthe quadrature modulator blocks is configured as a pulse code modulatoror a pulse width modulator. By using pulse code modulators or pulsewidth modulators in this way, the performance of the modulators may beoptimized.

In a fifth possible implementation form of a signal processingarrangement according to the fourth possible implementation form, thelast of the cascaded in-phase modulator blocks and/or the last of thecascaded quadrature modulator blocks is configured as a sigma-deltamodulator. By having a different modulation for the last in-phasemodulator block and/or the last quadrature modulator block, the smallsignal close band signal to noise ratio performance improved for thesignal processing arrangement for some operational modes. Also, as theinput signal of the last in-phase modulator block and/or the lastquadrature modulator block will have a short input bit length itsinternal functional blocks can be simplified. This saves design area andincrease processing speed.

In a sixth possible implementation form of a signal processingarrangement according to any one of the second to fifth possibleimplementation forms, each in-phase modulator block, except the last ofthe cascaded in-phase modulator blocks, is configured to provide anerror signal between its input signal and its resulting modulatedin-phase signal to the succeeding in-phase modulator block; and/or eachquadrature modulator block, except the last of the cascaded quadraturemodulator blocks, is configured to provide an error signal between itsinput signal and its resulting modulated quadrature signal to thesucceeding quadrature modulator block. By such an arrangement of thein-phase modulator blocks, and/or the quadrature modulator blocks a flatnoise shaping may be provided.

In a seventh possible implementation form of a signal processingarrangement according to the sixth possible implementation form, eachin-phase modulator block, except the last of the cascaded in-phasemodulator blocks, is configured to scale its error signal beforeproviding it to the succeeding in-phase modulator block; and/or eachquadrature modulator block, except the last of the cascaded quadraturemodulator blocks, is configured to scale its error signal beforeproviding it to the succeeding quadrature modulator block. By thisfeature the circuit design will be simplified.

In an eighth possible implementation form of a signal processingarrangement according to any one of the second to the seventh possibleimplementation forms, each in-phase modulator block is configured tooutput the resulting modulated in-phase signal I_(SMn) calculableaccording to the following formula:

$I_{SMn} = \frac{{Round}\mspace{14mu}\left( {I_{SSn} \cdot 0.5 \cdot k_{n}} \right)}{0.5 \cdot k_{n}}$where I_(SMn) is the resulting modulated in-phase signal from the n:thin-phase modulator block, k_(n) is a predetermined n:th scale value,I_(SSn) is the input signal to the n:th in-phase modulator block andRound means that the value is rounded to the nearest integer value;and/or each quadrature modulator block is configured to output theresulting modulated quadrature signal Q_(SMn) calculable according tothe following formula:

$Q_{SMn} = \frac{{Round}\mspace{14mu}\left( {Q_{SSn} \cdot 0.5 \cdot k_{n}} \right)}{0.5 \cdot k_{n}}$where Q_(SMn) is the resulting modulated quadrature signal from the n:thquadrature modulator block, k_(n) is a predetermined n:th scale value,Q_(SSn) is the input signal to the n:th quadrature modulator block andRound means that the value is rounded to the nearest integer value.

A hardware realization of the in-phase modulator blocks and thequadrature modulator blocks will only have to perform add and subtractoperations and no multiply operation. By such an arrangement a highmodulation speed and a small circuit design area may be achieved. Theinter-stage multipliers k₁-k₄ are preferably a power of 2 value. Such achoice simplifies the multiply operation into a bit shift operation.

A ninth possible implementation form of a signal processing arrangementaccording to any one of the second to the eighth possible implementationforms, further comprises a corresponding digital pre-distorter for eachin-phase modulator block, wherein each digital pre-distorter isconfigured to compensate for non-linearity errors in the input signal toits corresponding in-phase modulator block; and/or a digitalpre-distorter for each quadrature modulator block, wherein each digitalpre-distorter is configured to compensate for non-linearity errors inthe input signal to its corresponding quadrature modulator block.

The use of digital pre-distorters provides more tunability of the signalprocessing arrangement.

In a tenth possible implementation form of a signal processingarrangement according to the first aspect or to any one of the first tothe ninth possible implementation forms, the in-phase harmonic filtercomprises in-phase harmonic filter blocks, and the quadrature harmonicfilter comprises quadrature harmonic filter blocks, wherein eachin-phase harmonic filter block is connected to a corresponding in-phasedemodulator block via a corresponding in-phase demodulator block, andeach quadrature harmonic filter block is connected to a correspondingquadrature modulator block via a corresponding quadrature demodulatorblock.

In an eleventh possible implementation form of a signal processingarrangement according to the tenth possible implementation form of thefirst aspect, each in-phase harmonic filter block comprises an in-phasefilter input configured to receive the demodulated in-phase signal andtwo-phase data shifters for processing of the demodulated in-phasesignal, wherein each two-phase data shifter comprises a first phase datashifter and a second phase data shifter; and/or each quadrature harmonicfilter block comprises a quadrature filter input configured to receivethe demodulated quadrature signal and two-phase data shifters forprocessing of the demodulated in-phase signal, wherein each two-phasedata shifter comprises a first phase data shifter and a second phasedata shifter.

With the above arrangement of the in-phase harmonic filter block and thequadrature harmonic filter block an effective filtering on harmonics inthe demodulated in-phase signal and on harmonics in the demodulatedquadrature signal is achieved.

In a twelfth possible implementation form of a signal processingarrangement according to the eleventh possible implementation form ofthe first aspect the in-phase harmonic filter blocks and the quadratureharmonic filter blocks are configured to operate in at least a firstmode; wherein in the first mode, in each in-phase harmonic filter blockthe two-phase data shifters are configured cascaded, and the firsttwo-phase data shifter is configured to receive the demodulated in-phasesignal from the in-phase filter input; and in each quadrature harmonicfilter block the two-phase data shifters are configured cascaded and thefirst two-phase data shifter is configured to receive the demodulatedquadrature signal from the quadrature filter input.

By the above configuration of the two-phase data shifters, the harmonicfilter blocks provide an efficient filtration of the in-phase signal andthe quadrature signal.

In a thirteenth possible implementation form of a signal processingarrangement according to the twelfth possible implementation form of thefirst aspect, in the first mode, the in-phase harmonic filter blocks andthe quadrature harmonic filter blocks are configured to shift thedemodulated in-phase signal from a first phase data shifter to thesubsequent first phase data shifter based on a first reference clocksignal and to shift data from a second phase data shifter to thesubsequent second phase data shifter based on a second reference clocksignal, wherein the first reference clock signal and the secondreference clock signal both have the same frequency.

By having two-phase data shifters the noise is further reduced incomparison to having only single phase data shifters.

In a fourteenth possible implementation form of a signal processingarrangement according the twelfth or thirteenth possible implementationform of the first aspect the in-phase harmonic filter blocks and thequadrature harmonic filter blocks are configured to operate in also in asecond mode; wherein in the second mode in each in-phase harmonic filterblock the two-phase data shifters are configured in parallel andconfigured to receive the demodulated in-phase signal from the in-phasefilter input, and in the quadrature harmonic filter blocks the two-phasedata shifters are connected in parallel to the quadrature filter input.

This second mode is adapted for the case when no modulation harmonicsare created.

A fifteenth possible implementation form of a signal processingarrangement according to the any possible implementation form of thefirst aspect or the first aspect as such comprises:

an up-conversion and mixing module connected to the in-phase harmonicfilter and the quadrature harmonic filter, and configured to up-convertand mix the in-phase digital signal and the quadrature digital signalinto an up-converted and mixed digital signal;

a serializer connected to the digital up-conversion and mixing module,and configured to serialize the up-converted and mixed digital signalinto serialized digital signals;

a power amplifier for each one of the serialized digital signals,wherein each power amplifier is configured to power amplify a serializeddigital signal and output the power amplified serialized digital signal.

By having a power amplifier for each one of the serialized digitalsignals the final combination, of the signal to be fed to an antenna, isperformed after the power amplifiers. Also the final stage of theharmonic filtering is performed after the power amplifiers and a powercombination network composed of switching capacitances. In this way thesignal is kept digital as long as possible.

In a sixteenth possible implementation form of a signal processingarrangement according to the fifteenth possible implementation form ofthe first aspect the in-phase modulator and the quadrature modulator areconfigured to operate at a modulation frequency, and the serializeddigital signals have a carrier frequency, wherein the in-phase harmonicfilter and the quadrature harmonic filter are configured to operate inthe first mode when the modulation frequency is different from thecarrier frequency, and to operate in the second mode when the modulationfrequency is equal to the carrier frequency. Thus, when the modulationfrequency is equal to the carrier frequency, and no modulation harmonicsare created, the in-phase harmonic filter and the quadrature harmonicfilter are configured to operate in the second mode in which nofiltration of harmonics occurs. When the modulation frequency isdifferent from the carrier frequency, the in-phase harmonic filter andthe quadrature harmonic filter are configured to operate in the firstmode in which filtration of harmonics occurs.

Thus, it is possible to have the signal processing arrangementconfigured to operate in only the first mode. If the modulationfrequency and the carrier frequency are controlled to always bedifferent there is no need for the signal processing arrangement to beable to operate in the second mode.

A second aspect of the present disclosure relates to a signal processingmethod comprising:

receiving an in-phase signal (I) and modulating the in-phase signal (I);

receive a quadrature signal (Q) modulating the quadrature signal (Q);

demodulating the modulated in-phase signal (I) and outputting ademodulated in-phase signal (I);

demodulating the modulated quadrature (Q) and outputting a demodulatedquadrature signal (Q);

performing a filtering on harmonics in the demodulated in-phase signal(I) and outputting an in-phase digital signal (I);

performing a filtering on harmonics in the demodulated quadrature signal(Q) and outputting a quadrature digital signal (Q).

The signal processing method may be supplemented by any of the featuresof the apparatuses described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows schematically a signal processing arrangement for atransmitter according to an embodiment of the present disclosure.

FIG. 2 shows schematically a transmitter comprising a signal processingarrangement according to a second embodiment of the present disclosure.

FIG. 3 shows schematically in more detail the transmitter in FIG. 2.

FIG. 4 shows in more detail the in-phase digital harmonic filter and thequadrature digital harmonic filter of the signal processing arrangementin FIG. 1, FIG. 2 and FIG. 3.

FIG. 5 shows in more detail the first in-phase harmonic filter block andthe first quadrature harmonic filter block in the transmitter in FIG. 3.

FIG. 6 shows schematically a transmitter device in a wirelesscommunication system which transmitter device comprises a signalprocessing arrangement according to FIG. 2.

DETAILED DESCRIPTION

In the following description embodiments of the disclosure the samereference numerals will be used for the same features in the differentdrawings.

FIG. 1 shows schematically a signal processing arrangement 100 for atransmitter (not shown in FIG. 1) according to an embodiment of thepresent disclosure. The signal processing arrangement 100 comprises anin-phase modulator 102 configured to receive an in-phase signal I andconfigured to modulate the in-phase signal I, and a quadrature modulator104 configured to receive a quadrature signal Q and configured tomodulate the quadrature signal Q. The signal processing arrangement 100also comprises an in-phase demodulator 140 configured to demodulate themodulated in-phase signal I_(M) and to output a demodulated in-phasesignal I_(DM), and a quadrature demodulator 142 configured to demodulatethe modulated quadrature signal Q_(M) and to output a demodulatedquadrature signal Q_(DM). Furthermore, the signal processing arrangement100 comprises an in-phase harmonic filter 106 configured to perform afiltering on harmonics in the demodulated in-phase signal I_(DM) and tooutput an in-phase digital signal I_(D) and a quadrature harmonic filter108 configured to perform a filtering on harmonics in the demodulatedquadrature signal Q_(DM) and to output a quadrature digital signalQ_(D). Preferably, the in-phase modulator 102 and the quadraturemodulator 104 are configured to perform pulse code modulation or pulsewidth modulation.

In operation, an in-phase signal I (e.g. derived from an IQ signal) isinput to the in-phase modulator 102 and a quadrature signal Q (e.g.derived from the IQ signal and synchronised to the in-phase signal I) isinput to the quadrature modulator 104. The in-phase signal I and thequadrature signal Q are e.g. at least 12 bit digital signals. Thein-phase modulator 102 modulates the in-phase signal I and outputs amodulated in-phase signal I_(M) to the in-phase demodulator 140. Thequadrature modulator 104 modulates the quadrature signal Q and outputs amodulated quadrature signal Q_(M) to the quadrature demodulator 142. Thein-phase demodulator 140 demodulates the modulated in-phase signal andoutputs a demodulated in-phase signal I_(DM) to the in-phase harmonicfilter 106. The in-phase harmonic filter 106 performs a filtering onharmonics in the demodulated in-phase signal I_(DM) and outputs anin-phase digital signal I_(D). The quadrature demodulator 142demodulates the modulated quadrature signal and outputs a demodulatedquadrature signal Q_(DM) to the quadrature harmonic filter 108. Thequadrature harmonic filter 108 performs a filtering on harmonics in thedemodulated quadrature signal Q_(DM) and outputs a quadrature digitalsignal Q_(D).

FIG. 2 shows schematically a transmitter 200 comprising a signalprocessing arrangement 100 according to an embodiment of the presentdisclosure. Only the differences between the signal processingarrangement 100 of FIG. 1 and the signal processing arrangement 100 ofFIG. 2 will be described. The transmitter 200 comprises a digitalup-sampling device 150 comprising an input 152. The digital up-samplingdevice 150 does not form part of the signal processing arrangement 100.The digital up-sampling device 150 is configured to receive a digitalinput signal S_(IN) on the input 152 and to up-sample and transform thedigital input signal into an in-phase signal I and a quadrature signalQ. The in-phase signal I and the quadrature signal Q are inputs to thein-phase modulator 102 and the quadrature modulator 104 as has beendescribed in connection with FIG. 1 above. Also the in-phase demodulator140, the quadrature demodulator 142, the in-phase harmonic filter 106and the quadrature harmonic filter 108 have been described in connectionwith FIG. 1.

The signal processing arrangement 100 also comprises an up-conversionand mixing module 116 connected to the in-phase harmonic filter 106 andthe quadrature harmonic filter 108. The up-conversion and mixing module116 is configured to up-convert and mix the in-phase digital signal andthe quadrature digital signal into an up-converted and mixed digitalsignal. The signal processing arrangement 100 also comprises aserializer 136 connected to the digital up-conversion and mixing module116, and configured to serialize the up-converted and mixed digitalsignal into serialized digital signals. Furthermore, the signalprocessing arrangement 100 comprises a power amplifier 110 for each oneof the serialized digital signals. Each power amplifier 110 isconfigured to power amplify a serialized digital signal and output thepower amplified serialized digital signal. The signal processingarrangement 100 may be manufactured as an integrated circuit. Thetransmitter 200 comprises the above described digital up-sampling device150. The transmitter 200 also comprises a power combination filter 112which combines the power amplified serialized digital signals into acombined output signal which is output to a load in the form of anantenna 114. The power combination filter 112 may be realized in a largenumber of ways and its function is to combine the power amplifiedserialized digital signals from the power amplifiers 110.

The digital up-sampling device 150 is driven by a first clock signalCLK1. Also the in-phase modulator 102 and the quadrature modulator 104are driven by the first clock signal CLK1. The frequency of the firstclock signal CLK1 is called the modulation frequency f_(s). The in-phasedemodulator 140 and the quadrature demodulator 142 are driven by asecond clock signal CLK2. The first clock signal CLK1 is equal to thesecond clock signal CLK2. I.e. the have the same frequency and phase.The in-phase harmonic filter 106 and the quadrature harmonic filter 108,are driven by a third clock signal CLK3 of a first phase PH1 and asecond phase PH2. The frequency of the third clock signal CLK3 is calledthe carrier frequency f_(c). Depending on the working mode the carrierfrequency f_(c) may be equal to or different from the modulationfrequency f_(s). The serializer 136 is driven by a fourth clock signalCLK4 having a frequency of 2 times the carrier frequency f_(c).

The final signal processing steps are performed in the power combinationfilter 112. The in-phase harmonic filter 106 is configured to realize apart of the signal processing steps necessary for filtering outmodulation harmonics in the demodulated in-phase signal I.Correspondingly, the quadrature harmonic filter 108 is configured torealize a part of the signal processing steps necessary for filteringout modulation harmonics in the demodulated quadrature phase signal Q.The remainder of the steps necessary for filtering out modulationharmonics in the demodulated in-phase signal and in the demodulatedquadrature signal Q are performed in the power combination filter 112after the up-conversion and mixing module 116, and after the serializer136. An antenna 114 is connected to the power combination filter 112.

FIG. 3 shows schematically in more detail the transmitter in FIG. 2. Ascan be seen in FIG. 3 the in-phase modulator 102 comprises cascadedin-phase modulator blocks 118, 118′, 118″, and the quadrature modulator104 comprises cascaded quadrature modulator blocks 122, 122′, 122″.Furthermore, the in-phase demodulator 140 comprises in-phase demodulatorblocks 146, 146′, 146″ and the quadrature demodulator 142 comprisesquadrature demodulator blocks 148, 148′, 148″. Each in-phase demodulatorblock 146, 146′, 146″, is connected to a corresponding in-phasemodulator block 118, 118′, 118″, and each quadrature demodulator blocks148, 148′, 148″, is connected to a corresponding quadrature modulatorblock 122, 122′, 122″. Each one of the in-phase modulator blocks 118,118′, 118″, is configured to provide a resulting modulated in-phasesignal to the corresponding in-phase demodulator block 146, 146′, 146″and each one of the quadrature modulator blocks 122, 122′, 122″ isconfigured to provide a resulting modulated quadrature signal to thecorresponding quadrature demodulator block 148, 148′, 148″.

The first and the second of the in-phase modulator blocks 118, 118′, areconfigured as a pulse code modulator or a pulse width modulator.Correspondingly, the first and the second of the quadrature modulatorblocks 122, 122′, 122″, are configured as a pulse code modulator or apulse width modulator. The last of the cascaded in-phase modulatorblocks 118″, and the last of the cascaded quadrature modulator blocks122″ are configured as a sigma-delta modulator. Alternatively, both ofthe last of the cascaded modulator blocks 118″ and 122″ could beconfigured as a pulse width modulator PWM or a pulse code modulator PCM.Each in-phase modulator block 118, 118′, except the last of the cascadedin-phase modulator blocks, is configured to provide an error signalbetween its input signal and its resulting modulated in-phase signal tothe succeeding in-phase modulator block 118′, 118″. Each quadraturemodulator block 122, 122′, except the last of the cascaded quadraturemodulator blocks, is configured to provide an error signal between itsinput signal and its resulting modulated quadrature signal to thesucceeding quadrature modulator block 122′, 122″. Furthermore, eachin-phase modulator block, except the last of the cascaded in-phasemodulator blocks, is configured to scale its error signal beforeproviding it to the succeeding in-phase modulator block, and eachquadrature modulator block, except the last of the cascaded quadraturemodulator blocks, is configured to scale its error signal beforeproviding it to the succeeding quadrature modulator block. Thus, themodulation in the in-phase modulator 102 is as follows from thedescription of FIG. 4 below.

Furthermore, the in-phase harmonic filter 106 comprises in-phaseharmonic filter blocks 120, 120′, 120″, and the quadrature harmonicfilter 108 comprises quadrature harmonic filter blocks 124, 124′, 124″,wherein each in-phase harmonic filter block 120, 120′, 120″ is connectedto a corresponding in-phase modulator block 118, 118′, 118″ via acorresponding in-phase demodulator block 146, 146′, 146″, and eachquadrature harmonic filter block 124, 124′, 124″ is connected to acorresponding quadrature modulator block 122, 122′, 122″ via acorresponding quadrature demodulator block 148, 148′, 148″. The in-phaseharmonic filter blocks 120, 120′, 120″, and the quadrature harmonicfilter blocks 124, 124′, 124″, will be described in more detail belowwith reference to FIG. 5.

As is also shown in FIG. 3 the up-conversion and mixing module 116comprises an in-phase up-conversion block 180, 180′, 180″, for eachin-phase harmonic filter block 146, 146′, 146″, and a quadratureup-conversion block 182, 182′, 182″, for each quadrature harmonic filterblock 148, 148′, 148″. The in-phase up-conversion blocks 180, 180′,180″, and the quadrature up-conversion blocks 182, 182′, 182″ up-convertthe filtered signals from the in-phase harmonic filter blocks 146, 146′,146″, and the quadrature harmonic filter blocks 148, 148′, 148″. A mixer184 is connected to the in-phase up-conversion blocks 180, 180′, 180″,and the quadrature up-conversion blocks 182, 182′, 182″. The mixer 184performs mixing of the different signal from the in-phase up-conversionblocks 180, 180′, 180″, and the quadrature up-conversion blocks 182,182′, 182″. The mixer is connected to a serializer 136, a powercombination filter 112, and an antenna 114 as has been described in FIG.2.

FIG. 4 shows in more detail the in-phase modulator with cascadedin-phase modulator blocks. The in-phase signal I is input to thein-phase modulator 102. As can be seen in FIG. 4 the in-phase modulator102 comprises four cascaded in-phase modulator blocks 118, 118′, 118″,118′″. The in-phase modulator also comprises a corresponding digitalpre-distorter 172, 172′, 172″, 172′″, for each in-phase modulator block,wherein each digital pre-distorter 172, 172′, 172″, 172′″, is configuredto compensate for non-linearity errors in the input signal to itscorresponding in-phase modulator block 118, 118′, 118″, 118′″. Thisrequires knowledge on the non-linearity errors in the input signal. Thequadrature modulator block is configured in a corresponding way and willnot be described in detail herein. Each in-phase modulator block 118,118′, 118″, 118′″, is configured to output a resulting modulatedin-phase signal I_(SMn) calculable according to the following formula:

$I_{SMn} = \frac{{Round}\mspace{14mu}\left( {I_{SSn} \cdot 0.5 \cdot k_{n}} \right)}{0.5 \cdot k_{n}}$where I_(SMn) is the resulting modulated in-phase signal from the n:thin-phase modulator block 118, 118′, 118″, k_(n) is a predetermined n:thscale value, I_(SSn) is the input signal to the n:th in-phase modulatorblock and Round means that the value is rounded to the nearest integervalue. Furthermore, the n:th in-phase modulator block 118, 118′, 118″,except the last in-phase modulator block 118′″ is configured tocalculate the input signal I_(SSn+1) to the following in-phase modulatorblock 118′, 118″, 118′″ according to the following formula:I _(SSn+1)=(I _(SSn) −I _(SMn))·k _(n).As mentioned above the quadrature modulator is configured in thecorresponding way. As an example we assume that the input signal I is0.3 and that all k_(n) are equal to 8. This means that the firstmodulated in-phase signal ISM1 from the first in-phase modulator block118 is equal to:

$I_{SMn} = \frac{{Round}\mspace{14mu}\left( {0.3 \cdot 0.5 \cdot 8} \right)}{0.5 \cdot 8}$i.e., I_(SM1)=0.25. Furthermore, the second input signal I_(SS2) to thesecond modulator block is (0.3−0.25)·8=0.4.

FIG. 5 shows in more detail the first in-phase harmonic filter block120. Each in-phase harmonic filter block 120, 120′, 120″, comprises anin-phase filter input 138, 138′, 138″, (FIG. 3), configured to receivethe demodulated in-phase signal. In FIG. 5 only the first in-phaseharmonic filter block 120 is shown. The other in-phase harmonic filterblocks have the same layout. The first in-phase harmonic filter block120 shown in FIG. 5 comprises two-phase data shifters 126, 126′, 126″,for processing of the demodulated in-phase signal. Each two-phase datashifter 126, 126′, 126″, comprises a first phase data shifter 128, 128′,128″, and a second phase data shifter 130, 130′, 130″. Correspondingly,each quadrature harmonic filter block 124, 124′, 124″, comprises aquadrature filter input 164, 164′, 164″ configured to receive thedemodulated quadrature signal. In FIG. 5 only the first quadratureharmonic filter block 124 is shown. The first quadrature harmonic filterblock 124 comprises two-phase data shifters for processing of thedemodulated in-phase signal. Each two-phase data shifter 166, 166′,166″, comprises a first phase data shifter 168, 168′, 168″, and a secondphase data shifter 170, 170′, 170″. A separate multiplexer unit MUX isarranged between the in-phase filter input 138 and each two-phase datashifter 126′, 126″ except the first two-phase data shifter 126, 126′,126″. Each multiplexer unit MUX is also arranged between a two-phasedata shifter and the previous two-phase data shifter 126′, 126″, and aprevious two-phase data shifter 126, 126′. A separate multiplexer unitMUX′ is arranged between the quadrature filter input 164 and eachtwo-phase data shifter 166′, 166″ except the first two-phase datashifter 166. Each multiplexer unit MUX′ is also arranged between atwo-phase data shifter 166′, 166″ and a previous two-phase data shifter166, 166′.

The in-phase harmonic filter blocks 120, 120′, 120″, and the quadratureharmonic filter blocks 124, 124′, 124″, are configured to operate in atleast a first mode. In the first mode, two-phase data shifters 126,126′, 126″ of the first in-phase harmonic filter blocks 120, areconfigured cascaded, and the first two-phase data shifter 126 isconfigured to receive the demodulated in-phase signal from the in-phasefilter input 138. The multiplexer units MUX are configured to connectthe data shifters 126, 126′, 126″, to provide the data shifter cascadedin this first mode. Thus, the in-phase filter input 138 is connectedonly to the first two-phase data shifter 126 in this first mode. Theother in-phase harmonic filter blocks 120′, 120″ (FIG. 3) are configuredin the same way. In the first mode the two-phase data shifters 166,166′, 166″ of the first quadrature harmonic filter block 124, 124′,124″, are configured cascaded and the first two-phase data shifter 166is configured to receive the demodulated quadrature signal from thequadrature filter input 164. The other quadrature harmonic filter blocks124′, 124″ (FIG. 3), are configured in the same way.

In the first mode, the in-phase harmonic filter blocks 120, 120′, 120″,and the quadrature harmonic filter blocks 124, 124′, 124″, areconfigured to shift the demodulated in-phase signal from a first phasedata shifter 126, 126′; 168, 168′, to the subsequent first phase datashifter 126′, 126″; 168′, 168″, based on a first reference clock signalCLK3 PH1, and to shift data from a second phase data shifter 130, 130′;170, 170′, to the subsequent second phase data shifter 130′, 130″; 170′,170″, based on a second reference clock signal CLK3 PH2, wherein thefirst reference clock signal CLK3 PH1 and the second reference clocksignal CLK3 PH2 both have the same frequency.

In the embodiment described with reference to FIG. 5, the in-phaseharmonic filter blocks 120, 120′, 120″, and the quadrature harmonicfilter blocks 124, 124′, 124″, are configured to operate also in asecond mode. This second mode is optional. In the second mode, in eachin-phase harmonic filter block 120, 120′, 120″, the two-phase datashifters 126, 126′, 126″, are configured in parallel and configured toreceive the demodulated in-phase signal from the in-phase filter input138, and, in the quadrature harmonic filter blocks 124, 124′, 124″, thetwo-phase data shifters 166, 166′, 166″, are connected in parallel tothe quadrature filter input 164. This is achieved by the multiplexerunits MUX being configured to connect the in-phase filter input 138 witheach one of the two-phase data shifters 126, 126′, 126″.

FIG. 6 shows schematically a transmitter device 300 in a wirelesscommunication system 400. The transmitter device 300 comprises atransmitter 100 according to FIG. 2 or FIG. 3. The wirelesscommunication system 400 also comprises a base station 500 which mayalso comprise a quadrature digital power amplifier system 100 accordingto any one of the embodiments described above. The dotted arrow A1represents transmissions from the transmitter device 300 to the basestation 500, which are usually called up-link transmissions. The fullarrow A2 represents transmissions from the base station 500 to thetransmitter device 300, which are usually called down-linktransmissions.

The present transmitter device 300 may be any of a User Equipment (UE)in Long Term Evolution (LTE), mobile station (MS), wireless terminal ormobile terminal which is enabled to communicate wirelessly in a wirelesscommunication system, sometimes also referred to as a cellular radiosystem. The UE may further be referred to as mobile telephones, cellulartelephones, computer tablets or laptops with wireless capability. TheUEs in the present context may be, for example, portable,pocket-storable, hand-held, computer-comprised, or vehicle-mountedmobile devices, enabled to communicate voice or data, via the radioaccess network, with another entity, such as another receiver or aserver. The UE can be a Station (STA), which is any device that containsan IEEE 802.11-conformant Media Access Control (MAC) and Physical Layer(PHY) interface to the Wireless Medium (WM).

The present transmitter device 300 may also be a base station a (radio)network node or an access node or an access point or a base station,e.g., a Radio Base Station (RBS), which in some networks may be referredto as transmitter, “eNB”, “eNodeB”, “NodeB” or “B node”, depending onthe technology and terminology used. The radio network nodes may be ofdifferent classes such as, e.g., macro eNodeB, home eNodeB or pica basestation, based on transmission power and thereby also cell size. Theradio network node can be a Station (STA), which is any device thatcontains an IEEE 802.11-conformant Media Access Control (MAC) andPhysical Layer (PHY) interface to the Wireless Medium (WM).

The invention claimed is:
 1. A signal processing apparatus for atransmitter, the signal processing apparatus comprising: an in-phasemodulator configured to receive an in-phase signal (I) and configured tomodulate the in-phase signal (I) to generate a modulated in-phase signal(I); a quadrature modulator configured to receive a quadrature signal(Q) and configured to modulate the quadrature signal (Q) to generate amodulated quadrature signal (Q); an in-phase demodulator coupled to thein-phase modulator and configured to: receive the modulated in-phasesignal (I) from the in-phase modulator; demodulate the modulatedin-phase signal (I) received from the in-phase modulator; and output ademodulated in-phase signal (I); a quadrature demodulator coupled to thequadrature modulator and configured to: receive the modulated quadraturesignal (Q) from the quadrature modulator; demodulate the modulatedquadrature signal (Q); and output a demodulated quadrature signal (Q);an in-phase harmonic filter coupled to the in-phase demodulator andcomprising in-phase harmonic filters, wherein each of the in-phaseharmonic filters is coupled to a corresponding in-phase demodulator, andwherein each of the in-phase harmonic filters is configured to performfiltering on harmonics in the demodulated in-phase signal (I) and tooutput a resulting in-phase digital signal (I); a quadrature harmonicfilter coupled to the quadrature demodulator and comprising quadratureharmonic filters, wherein each of the quadrature harmonic filters iscoupled to a corresponding quadrature demodulator, and wherein each ofthe quadrature harmonic filters is configured to perform filtering onharmonics in the demodulated quadrature signal (Q) and to output aresulting quadrature digital signal (Q).
 2. The signal processingapparatus of claim 1, wherein the in-phase modulator and the quadraturemodulator are configured to perform pulse code modulation or pulse widthmodulation.
 3. The signal processing apparatus of claim 1, wherein thein-phase modulator comprises cascaded in-phase modulators, wherein thequadrature modulator comprises cascaded quadrature modulators, whereineach of the cascaded in-phase modulators is configured to provide aresulting modulated in-phase signal to the in-phase demodulator, andwherein each of the cascaded quadrature modulators is configured toprovide a resulting modulated quadrature signal to the quadraturedemodulator.
 4. The signal processing apparatus of claim 3, wherein thein-phase demodulator comprises in-phase demodulators, wherein each ofthe in-phase demodulators is coupled to a corresponding in-phasemodulator, wherein the quadrature demodulator comprises quadraturedemodulators, and wherein each of the quadrature demodulators is coupledto a corresponding quadrature modulator.
 5. The signal processingapparatus of claim 3, wherein at least one of the cascaded in-phasemodulators is configured as a first pulse code modulator or a firstpulse width modulator, and wherein at least one of the cascadedquadrature modulators is configured as a second pulse code modulator ora second pulse width modulator.
 6. The signal processing apparatus ofclaim 5, wherein a last of the cascaded in-phase modulators and a lastof the cascaded quadrature modulators are each configured as asigma-delta modulator.
 7. The signal processing apparatus of claim 3,wherein each cascaded in-phase modulator except a last of the cascadedin-phase modulators is configured to provide an in-phase error signalbetween an input signal and a resulting modulated in-phase signal to asucceeding cascaded in-phase modulator, and wherein each cascadedquadrature modulator except a last of the cascaded quadraturemodulators, is configured to provide a quadrature error signal betweenan input signal and a resulting modulated quadrature signal to asucceeding cascaded quadrature modulator.
 8. The signal processingapparatus of claim 7, wherein each cascaded in-phase modulator exceptthe last of the cascaded in-phase modulators is configured to scale thein-phase error signal before providing the in-phase error signal to thesucceeding cascaded in-phase modulator, and wherein each cascadedquadrature modulator except the last of the cascaded quadraturemodulators is configured to scale the quadrature error signal beforeproviding the quadrature error signal to the succeeding cascadedquadrature modulator.
 9. The signal processing apparatus of claim 3,wherein the resulting modulated in-phase signal is a resulting modulatedin-phase signal I_(SMn) according to the following formula:$I_{SMn} = \frac{{Round}\mspace{14mu}\left( {I_{SSn} \cdot 0.5 \cdot k_{n}} \right)}{0.5 \cdot k_{n}}$where I_(SMn) is the resulting modulated in-phase signal from an n:thcascaded in-phase modulator, k_(n) is a predetermined n:th scale value,I_(SSn) is an input signal to the n:th cascaded in-phase modulator andRound means rounding to a nearest integer value, and wherein theresulting modulated quadrature signal is a resulting modulatedquadrature signal Q_(SMn) according to the following formula:$Q_{SMn} = \frac{{Round}\mspace{14mu}\left( {Q_{SSn} \cdot 0.5 \cdot k_{n}} \right)}{0.5 \cdot k_{n}}$where Q_(SMn) is the resulting modulated quadrature signal from the n:th cascaded quadrature modulator, k_(n) is a predetermined n:th scalevalue, Q_(SSn) is the input signal to the n:th cascaded quadraturemodulator and Round means rounding to the nearest integer value.
 10. Thesignal processing apparatus of claim 3, further comprising: acorresponding digital pre-distorter coupled to a corresponding in-phasemodulator, wherein each digital pre-distorter is configured tocompensate for non-linearity errors in an input signal to itscorresponding in-phase modulator; and a digital pre-distorter coupled toa corresponding quadrature modulator, wherein each digital pre-distorteris configured to compensate for non-linearity errors in the input signalto its corresponding quadrature modulator.
 11. The signal processingapparatus of claim 1, wherein each of the in-phase harmonic filterscomprises an in-phase filter input configured to receive the demodulatedin-phase signal and first two-phase data shifters for processing of thedemodulated in-phase signal, wherein each of the first two-phase datashifters comprises a first phase data shifter and a second phase datashifter, wherein each quadrature harmonic filter block comprises aquadrature filter input configured to receive the demodulated quadraturesignal and second two-phase data shifters for processing of thedemodulated in-phase signal, and wherein each of the second two-phasedata shifters comprises a first phase data shifter and a second phasedata shifter.
 12. The signal processing apparatus of claim 11, whereinthe in-phase harmonic filters and the quadrature harmonic filters areconfigured to operate in at least a first mode, wherein in the firstmode: in each of the in-phase harmonic filters, the first two-phase datashifters of the in-phase harmonic filter are cascaded, and the firsttwo-phase data shifters of the in-phase harmonic filter are configuredto receive the demodulated in-phase signal from the in-phase filterinput; and in each of the quadrature harmonic filters, the secondtwo-phase data shifters of the quadrature harmonic filter are cascaded,and the first two-phase data shifters of the quadrature harmonic filterare configured to receive the demodulated quadrature signal from thequadrature filter input.
 13. The signal processing apparatus of claim12, wherein in the first mode, the in-phase harmonic filters and thequadrature harmonic filters are configured to shift the demodulatedin-phase signal from a first phase data shifter to a subsequent firstphase data shifter based on a first reference clock signal (CLK1) and toshift data from a second phase data shifter to a subsequent second phasedata shifter based on a second reference clock signal (CLK2), andwherein the first reference clock signal (CLK1) and the second referenceclock signal (CLK2) both have a same frequency.
 14. The signalprocessing apparatus of claim 12, wherein the in-phase harmonic filtersand the quadrature harmonic filters are further configured to operate ina second mode, wherein in the second mode: in each of the in-phaseharmonic filters, the first two-phase data shifters of the in-phaseharmonic filter are configured in parallel and configured to receive thedemodulated in-phase signal from the in-phase filter input; and in eachof the quadrature harmonic filters, the first two-phase data shiftersare coupled in parallel to the quadrature filter input.
 15. The signalprocessing apparatus of claim 1, further comprising: an up-converter andmixer coupled to the in-phase harmonic filter and the quadratureharmonic filter, wherein the up-converter and mixer is configured toup-convert and mix the in-phase digital signal and the quadraturedigital signal into an up-converted and mixed digital signal; aserializer coupled to the up-converter and mixer, wherein the serializeris configured to serialize the up-converted and mixed digital signalinto serialized digital signals; and a power amplifier for each of theserialized digital signals, wherein each power amplifier is configuredto power amplify a serialized digital signal and output a poweramplified serialized digital signal.
 16. The signal processing apparatusof claim 15, wherein the in-phase harmonic filters and the quadratureharmonic filters are configured to operate in at least a first mode anda second mode, wherein the in-phase modulator and the quadraturemodulator are configured to operate at a modulation frequency (f_(s)),wherein the serialized digital signals have a carrier frequency (f_(c)),wherein the in-phase harmonic filter and the quadrature harmonic filterare configured to operate in the first mode when the modulationfrequency (f_(s)) is equal to the carrier frequency (f_(c)), and whereinthe in-phase harmonic filter and the quadrature harmonic filter areconfigured to operate in the second mode when the modulation frequency(f_(s)) is different from the carrier frequency (f_(c)).
 17. The signalprocessing apparatus of claim 1, wherein the in-phase modulator, thequadrature modulator, the in-phase demodulator, the quadraturedemodulator, the in-phase harmonic filter, and the quadrature harmonicfilter are transmission components.
 18. A signal processing method,comprising: receiving, by an in-phase modulator, an in-phase signal (I);modulating, by the in-phase modulator, the in-phase signal (I);receiving, by a quadrature modulator, a quadrature signal (Q);modulating, by the quadrature modulator, the quadrature signal (Q);receiving, by an in-phase demodulator from the in-phase modulator, amodulated in-phase signal (I); demodulating, by the in-phasedemodulator, the modulated in-phase signal (I); outputting, by thein-phase demodulator, a demodulated in-phase signal (I); receiving, by aquadrature demodulator from the quadrature modulator, a modulatedquadrature signal (Q); demodulating, by the quadrature demodulator, themodulated quadrature signal (Q); outputting, by the quadraturedemodulator, a demodulated quadrature signal (Q); performing, by anin-phase harmonic filter comprising in-phase harmonic filters, filteringon harmonics in the demodulated in-phase signal (I), wherein each of thein-phase harmonic filters is coupled to a corresponding in-phasedemodulator; outputting a resulting in-phase digital signal (I) based onperforming the filtering on harmonics in the demodulated in-phase signal(I); performing, by a quadrature harmonic filer comprising quadratureharmonic filters, filtering on harmonics in the demodulated quadraturesignal (Q), wherein each of the quadrature harmonic filters is coupledto a corresponding quadrature demodulator; and outputting a resultingquadrature digital signal (Q) based on performing the filtering onharmonics in the demodulated quadrature signal (Q).
 19. The method ofclaim 18, wherein the in-phase modulator comprises cascaded in-phasemodulators, wherein the quadrature modulator comprises cascadedquadrature modulators, and wherein the method further comprises:providing, by each of the cascaded in-phase modulators, a resultingmodulated in-phase signal to the in-phase demodulator; and providing, byeach of the cascaded quadrature modulators, a resulting modulatedquadrature signal to the quadrature demodulator.
 20. The method of claim18, further comprising performing, by each of the in-phase modulator andthe quadrature modulator, pulse code modulation or pulse widthmodulation.